"People make polyester out of oil. You take the oil, which is a kind of very big hydrocarbon molecule, and break it down into two smaller molecules, ethylene glycol and dimethyl naphthalate. These molecules are still made entirely of oxygen, carbon, and hydrogen atoms. Dimethyl terephthalate is an ester, and ethylene glycol is a kind of alcohol. When you mix the ester and the alcohol together, they form molecules with both positive and negative charges. The charges force the molecules to line up in chains of crystals that hold together as long fibers."
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Why is polyester and plastic so widely used?